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ENGINEERING, CS 2019 HSC 21d

A pictorial sketch of a laminated timber beam used in a bus shelter is shown. This beam has a second moment area of . The maximum applied bending moment is 17 kNm.
 

  1. Calculate the maximum bending stress present in the beam.   (3 marks)
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Second Moment of Area ()

Maximum Bending Moment ()

Distance (Neutral axis → outside of beam) = 125 mm

 
   
   

ENGINEERING, CS 2018 HSC 23c

The chassis for a motor vehicle could be made from a solid steel bar or hollow steel tube. Both the bar and the tube have the same mass and cost per metre.
 

Justify why a hollow tube would be used in preference to a solid bar to build the vehicle chassis.   (3 marks)

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→ Hollow tube has a higher second moment of area and is therefore more rigid.

→ Because the chassis is exposed to continual flexural forces and moments when the vehicle is moving, rigidity is important.

→ Stiffness is therefore a major design requirement.

→ The hollow tube also provides damage protection for any electrics cabling.

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→ Hollow tube has a higher second moment of area and is therefore more rigid.

→ Because the chassis is exposed to continual flexural forces and moments when the vehicle is moving, rigidity is important.

→ Stiffness is therefore a major design requirement.

→ The hollow tube also provides damage protection for any electrics cabling.

♦♦ Mean mark 35%.